The world is facing problems such as the gradual extraction and depletion of petroleum reserves, and changes to the earth's atmosphere due to the greenhouse effect. In order to ensure the sustainability of human life, it has become a world trend to gradually decrease the use of petrochemical energy and petroleum feedstock and to develop new sources of renewable energy and materials.
Lignocellulose is the main ingredient of biomass, which is the most abundant organic substance in the world. Lignocellulose mainly consists of 38-50% cellulose, 23-32% hemicellulose and 15-25% lignin. Cellulose generates glucose through hydrolysis. However, it is difficult for chemicals to enter the interior of cellulose molecules for depolymerization due to strong intermolecular and intramolecular hydrogen bonding and Van de Waal forces and the complex aggregate structure of cellulose with high-degree crystallinity. The main methods of hydrolyzing cellulose are enzyme hydrolysis and acid hydrolysis. However, there is significant imperfection in these two technologies, therefore, it is difficult to apply widely.
Generally speaking, enzyme hydrolysis can be carried out at room temperature, which is an environmentally friendly method due to the rarity of byproducts, no production of anti-sugar fermentation substances, and integration with the fermentation process. However, a complicated pretreatment process is required, hydrolytic activity is low, the reaction rate is slow, and cellulose hydrolysis enzyme is expensive.
Dilute acid hydrolysis generally uses comparatively cheap sulfuric acid as a catalyst, but it must operate in a corrosion-resistant pressure vessel at more than 200° C., requiring high-level equipment; simultaneously, the temperature of the dilute acid hydrolysis is high, the byproduct thereof is plentiful, and the sugar yield is low. Concentrated acid hydrolysis can operate at lower temperature and normal pressure. However, there are problems of strong corrosivity of concentrated acid, complications in the post-treatment process of the hydrolyzed solution, large consumption of acid, and difficulties with recycling, among other drawbacks.